The image replaces Nike's advertising slogan "Just Do It" with, "NATO Air Just Do It" and depicts a warplane.

It was originally posted on her Twitter profile by Vlora Citaku, a member of the government in Priština, and then picked up and retweeted by Oana Lungescu, a spokesperson for the western military alliance, on her official account.

It came on the day marking the 15th anniversary since the start of NATO's 1999 bombing campaign against Serbia.

The Serbian Ministry of Foreign Affairs said late on Monday that the gesture was disrespectful toward those Serbians killed by NATO during the 78-day war. It also said that "such moves do not contribute to the cooperation between Serbia and the alliance."

The ministry noted in its statement that March 24 is also marked remembrance day for the victims of the NATO bombing campaign, and that Assistant Foreign Minister Miomir Udovički discussed the matter with NATO's military liaison office chief in Belgrade.

Serbia's diplomatic representatives in Brussels also spoke with NATO representatives, the ministry said, and told them that "such actions show disrespect for the Serb victims of NATO's bombing, and do not contribute to the cooperation between Serbia and NATO that is realized through the NATO program Partnership for Peace."

NATO's spokesperson, however, maintains that it was appropriate for her to retweet the image on the same day. Late on Monday, Lungescu defended the gesture by saying that the retweet "in no way had the goal of disrespecting the victims of the 1999 conflict."

Instead, said she, it was "a retweet of a tweet thanking NATO for saving civilians from ethnic cleansing in Kosovo. NATO reacted quickly to protect people in Kosovo in 1999 and our peace mission KFOR continues to provide a safe environment for all people in Kosovo based on UN Security Council Resolution 1244."

In Belgrade, the Serbian government's Office for Kosovo issued a statement of its own, saying that the NATO spokesperson had posted "a cynical, sarcastic, and inhuman greeting."

When reached for comment, the U.S. sportswear manufacturer said that they "took their brand and slogan very seriously."

In response to a letter sent by several individuals from Serbia, including television producer Jakša Ščekić, Nike also said that the image "did not represent their officials stand" - and that company was in no way involved in posting the tweet or in creating the image.